Cestoplanidae Lang, 1884

Cestoplanidae Lang, 1884 View in CoL

Traditionally, the family has been included in Acotylea, despite several cotylean-like characters (e.g. male complex located posterior to the male pore and directed forward, male atrium wall folded to form a penis sheath, absence of Lang’s vesicle, posterior adhesive cells and cement/shell glands). Applying the cotylean diagnostic traits outlined above to Cestoplana rubrocincta (Grube, 1840) allows for reassignation of the family to Cotylea. This placement is strongly supported by our molecular analysis, which clearly reveals its cotylean status. This reclassification is further backed by earlier calls for a more careful examination of the posterior adhesive cells described for Cestoplana rubrocincta ( Lang, 1884) , by the description of cotylean-type male and female reproductive systems ( Laidlaw, 1903; Faubel , 1983) and by the findings of Bahia et al. (2017). Furthermore, because our 28S rDNA sequences of Cestoplana rubrocincta and Cestoplana australis Haswell, 1907 were largely identical, we confirm that Cestoplana australis is indeed a junior synonym of Cestoplana rubrocincta .

Cestoplanoidea was erected by Prudhoe (1985) to include the monospecific Diplopharyngeatidae ( Diplopharyngeata filiformis ) and the monogeneric Emprosthopharyngidae (six species). However, as previously mentioned, Diplopharyngeata filiformis belongs to Euplanidae and Emprosthopharynx has been removed to Stylochoplanidae ( Faubel, 1983) . Cestoplanidae then is the sole remaining family in Cestoplanoidea and, unlike Bahia et al. (2017), we argue that until a close sister family is described, elevating a single family to the level of a superfamily is not warranted.

Boniniidae Bock, 1923 View in CoL , Theamatidae Marcus, 1949 View in CoL and Amyellidae Faubel, 1984 View in CoL

Laumer & Giribet (2014) included eight polyclad species in their global phylogeny of rhabditophoran platyhelminths. Although their resulting polyclad subtree revealed two distinct clusters in Polycladida View in CoL , the selected species do not separate into Acotylea and Cotylea (sensu Lang, 1884; sensu Faubel , 1983, 1984). Specifically, their cotylean clade included Theama sp. that was traditionally placed into Acotylea ( Marcus, 1949). This led the authors to question the usefulness of the subordinal division of polyclads.

Faubel (1983) had already doubted the acotylean placement of Theamatidae View in CoL owing to the cotyleanlike features of the taxon (e.g. lack of Lang’s vesicle and presence of cement gland pouches), and recently, Bahia et al. (2017) transferred Theama sp. to Cotylea to be included in their new superfamily Chromoplanoidea . According to these authors, Chromoplanoidea contained the families Boniniidae View in CoL , Theamatidae View in CoL , Chromoplanidae View in CoL and Amyellidae View in CoL represented by Boninia divae Marcus & Marcus, 1968 View in CoL , Theama sp. , Chromoplana sp. and Chromyella sp. , respectively. However, in their analysis, the authors specifically excluded Chromoplana sp. from their phylogeny on the basis of ‘discrepant sequences’ ( Bahia et al., 2017: 657). As a result, Chromoplanoidea (sensu Bahia et al., 2017) no longer included its type family Chromoplanidae View in CoL , invalidating the superfamily.

Adding a new Theama sp. sequence plus several new Boninia View in CoL sequences ( Boninia antillarum (Hyman 1955) View in CoL and Boninia neotethydis Curini-Galletti & Campus, 2007 View in CoL ), we also recover a monophyletic clade of Boniniidae View in CoL + Theamatidae View in CoL + Chromyella sp. Currently, these species appear to be defined by a small, elongate body size and a combination of acotylean and cotylean traits associated with the reproductive structures. However, the slender body size is most probably attributable to ecological convergence rather than being of taxonomic importance, and other polyclads (e.g. cestoplanids) also possess acotylean and cotylean reproductive features. Even though Boniniidae View in CoL + Theamatidae View in CoL + Amyellidae View in CoL cluster together, in the absence of morphological synapomorphies we contend that it is premature to unite these species into a superfamilial taxon.

Since Bock’s (1923) description of Boninia mirabilis Bock, 1923 , three additional species have been described in the genus, two of which have type localities in the Caribbean. However, even Bock (1923) already noted unique, and for cotyleans atypical, traits of Boninia . Unlike cotyleans, they possess Lang’s vesicle, which led Hyman (1955a) to place B. antillarum ( Adenoplana antillarum Hyman, 1955 ) in Acotylea. Additionally, their sperm morphology resembles that of acotylean sperm ( Liana & Litvaitis, 2007, 2010) and they develop via an aberrant Müller’s larva reminiscent of an acotylean Götte’s larva ( Bolaños, 2008). Despite these acotylean-like traits, our molecular analysis confirms the placement of Boniniidae into Cotylea. Morphologically, placement of Boniniidae into Cotylea is supported by characters associated with the nervous system ( Quiroga et al., 2015). In Cotylea, globuli cell masses, which are aggregates of sensory ganglions, tend to be little defined or absent. The globuli cell masses of B. antillarum are poorly differentiated, similar to those found in some species of euryleptids, prosthiostomids and pseudocerotids ( Quiroga et al., 2015). Furthermore, the unique organization of the central nervous system, submerged in the longitudinal musculature, is an apomorphy for Boninia ( Quiroga et al., 2015) . Further analyses of nervous system anatomy in Theamatidae and Amyellidae might lend additional support to the monophyly of the clade.

Currently, two species of Boninia are recognized in the Caribbean. Boninia antillarum was described by Hyman (1955a), with the type locality in the US Virgin Islands. Marcus & Marcus (1968) extended the distribution to Curaçao and Bonaire and added B. divae (type locality in Curaçao), which is syntopic with B. antillarum . The authors justify a second species based on the arrangement of the cerebral eyes and the number of prostatoid organs. Specifically, B. antillarum is distinguished from B. divae by three anterior groups of cerebral eyes plus a fourth group further posterior, whereas the arrangement in B. divae is as two elongated longitudinal bands of cerebral eyes ( Marcus & Marcus, 1968: figs 61 and 67, respectively). Additionally, B. antillarum has <30 prostatoid organs, whereas B. divae has> 50 ( Fig. 7A). However, both traits co-vary with the age of the specimens, which can be gleaned by reported lengths of B. antillarum as 16 mm and of B. divae as 30–50 mm ( Marcus & Marcus, 1968).

We collected> 50 specimens of Boninia (including specimens from the type localities).Attempting to follow Marcus & Marcus (1968), we divided our specimens into B. divae and B. antillarum based on cerebral eye arrangement. However, nucleotide sequences of all our specimens were largely identical, regardless of initial species assignment or collection locality. Hence, we conclude that B. divae is not a separate species but instead a variant of B. antillarum and that the diagnostic characters proposed by Marcus & Marcus (1968) are not sufficient for species separation in the genus. Boninia divae then becomes a junior synonym of B. antillarum . We established monophyly of the genus Boninia with the inclusion of B. neotethydis in our phylogeny.